Alternator Breaker Pops

Hi everyone. In my new-to-me RV6A, as far as electrical goes, I have:

1. Added a cable connector to the battery terminals so that I can hook up a battery tender. This works very well and is in no danger of creating a short

2. Last night I left the master on (but all other electronics were off). When I got in the plane this morning, my v-meter read 11.4v, and it was enough to start the plane.

Nothing else, whatsoever, has been done to anything electrical.

When I started the plane (on its own power, it struggled to turn over but caught right away), I noticed the v-meter was still reading 11.4v. I also noticed the (60a) breaker was popped. I pushed it back in and all seemed fine. THIS SHOULD BE A VERY SIGNIFICANT DETAIL. Why would the breaker pop if all I did was leave the master on and put almost zero load on the system?

I wanted to charge the battery back up so I went into the pattern and after the first pattern, the breaker popped again. I pushed it back in one more time and in the pattern it was putting out 13.2v, which above 1500rpm may be low.

So, what I am hoping I can get is an "oh, yeah that's because you... just do this."

If anyone has insight into what may have happened here, I would genuinely appreciate it. At this point, I am literally begging anyone who responds to stay absolutely laser focused on the things I have mentioned in the notes, above. I'm not pulling the alternator to get it bench checked and I'm not replacing breakers until I have fully fleshed out the above.

I did, of course, de-cowl the plane and found no loose or disconnected wires and the belt is on tight. Everything "appears" normal.

I sure appreciate you folks. Thanks for your time.

What kind of battery? If it is an EarthX, it can take huge amounts of charging current when low, and could have asked for more than 60 Amps, which can pop that breaker.

Even a normal battery will draw a huge number of Amps when very low - so you could still have popped that breaker. And….the beaker could be propping at less than 60 Amps if it is weak or old.

I’d run it long enough to fully charge the battery, as indicated by the charge current topping off, and seeing only normal avionics loads on the Amp meter. Then se if the breaker will stay in.

What battery do you have? I have seen the EarthX batteries when they get low, they pull so much amps abs could trip the breaker. Do you have an amp gauge to see how much it’s charging? Or only a volt meter? My advice (it’s only worth what you are paying for it, which is nothing) is to charge the battery and try it again. A second less desirable option is to let the plane run for a while at low RPM so that the battery charges off the alternator on reduced volts and amps. It’s always best to remove the battery, service it if the caps are removable, and charge out of the plane though, as making the alternator do all the work may take some life out of it.

Okay, please forgive me for being direct, but it’s not real cool to ask for help and, in the same post, say what you won’t do. In fact, if you took it to a shop, they might very well replace the alternator or the CB, because their labor costs are so high that a ‘shotgun replace parts’ approach is often the cheapest. Now, assuming your labor is free:
What alternator do you have? If it’s a 60 amp alternator then the CB (and wiring) should be rated for more than that.
Do you have a standard ‘master contactor (relay)’? These things alone draw several amps, which is why your battery was low after draining overnight. Standard alternators/regulators do not follow the ideal charging voltages/currents for re-charging a nearly dead battery. Best practice would have been a multi-hour recharge on a good programable charger. I know some people who would advocate throwing your battery away, saying it will never re-gain full capacity.
So here’s what I would do:
Put the battery (I assume it’s a standard lead-acid?) on a good charger, until it’s fully charged. Ideally, if you have access to a load tester (a lot of car shops have one), do that. Otherwise, put it back into the plane, turn on the master (and whatever you need to read the buss voltage). If in less than a minute the voltage drops below 12 volts, your battery is toast. Get a new one. If everything looks good, start and go fly. Your buss voltage should be around 14.3 volts. Older systems often were set for 13.6 volts, but most modern batteries perform better at the higher number. If you have a sealed cell battery like an Odyssey, 14 volts is the bare minimum (slightly different chemistry). If all looks okay, you’re all set for vfr. If ifr in an electrically dependent airplane, I wouldn’t sleep until it passed a load test, or there were backup batteries, etc.

We all wish it was that simple

So, what I am hoping I can get is an "oh, yeah that's because you... just do this."

Click to expand...

Maybe you can provide a few more details, what kind of battery? how old is it?
Leaving the master on will drain your battery, the master relay consumes enough power to drain a battery until it is completely dead if you have it on long enough. Batteries don't always die at once but are slowly murdered by a number of issues including battery tenders.
Leaving the master on may have damaged the battery enough to short it out causing an overload on your charging system and popping the main breaker.
I wish I could provide you with a "laser focused reply" to solve your issue but for starters I would fully charge the battery on the ground and see if it fully recovers?
If it doesn't you'll have your problem solved with a new battery.

Master ON

If you are using a standard master contactor, the coil will draw around an amp or so continuously. If you left it ON over night, that load is likely the culprit...

What is open circuit voltage after sitting 12 hr post charging

For an Odessey battery, If it is greater than 12.9V it has accepted a charge,….
If not,…probably time to think about replacement


The fact that it cranked and started opens up the possibility that you did not totally trash the battery,…..


Recommend taking a look at the Mfr technical info

P.s. all good info from others above as to impact of low battery on breaker

Just me

If it is NOT a Li-ion battery, and the circuit breaker pops on flying, i say the battery is toast with probably a shorted cell.

If it IS an Li-ion battery, it might pop when first started but should settle down after a while and never pop again, if it pops again, then check the battery idiot lights.

JMHO

Matt,

Some thoughts:
- Yes, you caused the problem by leaving the master on.
- I assume you have a 60amp alternator. Any decent 60amp alternator will produce more than 60 amps given enough load. So when you put your depleted battery on it the battery pulled enough to pop your 60 amp breaker. To use and alternator output breaker you need to size it correctly. In this application that would be 70 amps. This will reduce such “nuisance” trips.
- Yes, you did abuse your battery so now you have very reduced confidence on it’s reserve capacity (as in it is likely it will no longer deliver the label plate amp-hrs). Replace it. Try to breath some life back into it with a charger but then use if for your law tractor or such. Side note - I replace one of my PC-625 batteries every three years - so neither battery is over six years old. I also replace any battery that has been abused (I left one of the two masters on once over the last 20 years).
- Your battery minder/tender/magic box will provide the best service if you use it only to charge the battery when you are physically there to monitor battery terminal voltage. These things tend to ruin a good battery if left on for long periods of time.

Carl